Production of metals



Aug. 12, 1958 M. P. HNILICKA, JR

PRODUCTION oF METALS Filed Oct. l5, 1954 2 Sheets-Sheet 1 Pump NGK?, Cooluni* Lil SSU`DDOCDDDDDCDDZ FIG.

MP m5 Ek.. VH N.l M H -01. /0 M ATTORNEY Aug. 12, 1958 M. P. HNlLlCKA, JR

PRODUCTION OF METALS 2 Sheets-Sheet 2 Filed OCl'.. l5, 1954 Ccoluni' Furnace ,fElecl'rlc FIG. 2

FIG. 3

INVENTOR Milo Hmll'ckn @QW w. M07@ ATTORNEY PRODUCTION F METAL'S Milo P. Hnilicka, Jr., Concord, Mass., assignor to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Application October 13, 1954, Serial No. 461,981 7 Claims. (Cl. 2156-34) This invention relates to the production of metals and more particularly to the production of refractory metals such as titanium and the like.

A principal object of the present invention is to provide an improved apparatus which is particularly adapted to the production of titanium and like metals by the reduction of a metal compound carried inafused salt.

Another object of the invention is to provide an vimproved apparatus of the above type which-is particularly adapted to large-scale operation with high rates of production.

Still another object of the presentinvention is to provide an improved apparatus of they above type which is particularly adapted for use with a process of the type described in the copending application -of Keller et al., Serial No. 373,512,1iled August 1l,- 1953.

Other objects of the invention. will in partpbe obvious and will in part appear hereinafter.

The invention accordingly comprises 4the apparatus possessing the construction, combination of elements and arrangement of. parts which are exemplified in= thefollowing detailed disclosure,v and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic drawing. 4illustratling one preferred embodiment of the invention;

Fig. 2 is a diagrammatic, enlarged detail vof aportion of Fig. 1; and

Fig. 3 is a diagrammatic, enlarged detail Iof another portion of Fig. 1.

In the production of metals such as.. titanium, as described in the aforementioned copendingapplication of Keller et al., it is preferred that the two-stage reduction of the titanium chloride be employed. In the first stage, sodium is preferably employed to reduce titanium tetrachloride to titanium dichloride which is dissolved in the byproduct sodium chloride. In the second stage, this solution is reduced to titanium metal. Itis also important that the second stage of the reduction be carried out gradually so that a relatively long time, is `4involved in the reduction of mass of dissolved lower titanium' chloride to titanium metal. It is also quite desirable that the two stages of the reduction be separated into two different pieces of equipment. Accordingly, eachrst'stage reactor is preferablyv arranged so vasto feed a number of second stage reactors. Since the secondstagereactors are preferably sequentially filled from .the first-stage reactor and are sequentially removed from the system-to provide for substantially continuous -operationof ,the first stage reactor, it is necessary to provide for isolation of the various second stage reactors from the lirststage-reactor.

These objectives of the inventionare achieved by providing a plurality of pipes which lead from .the first stage reactor to the various second stage reactors, therebeing one such pipe for each second stage reactor. 'In'v a r-r' ICC preferred embodiment, a portion of each of these pipes is :higher than the bottom of the lir'st stage reactor so that the molten s alt flowing from the first stage reactor to ,one of the second stage reactors 4must tlow upwardly in this portion. The apparatus also preferably `includes means for providing a sufficient gas pressure on the surface of the molten salt in the high portion of each pipe vto overcome the hydrostatic salt pressure from the reacvtor and to thereby stop the ow of salt through the pipe.

Associated .with each pipe is a means for freezing the n pipe which has thus been immobilized. This arrangev and the like.

ment permits the formation of a solid salt plug which completely isolates the rst stage reactor from that second stage reactor fed by the plugged pipe. This permits removal of the second stage reactor for emptying, cleaning When flow is to be resumed through the plugged pipe, the plug is melted by a suitable mechanism and the pres'suIe-equalizing mechanism is adjusted so as i to again permit ilow of molten salt upwardly in the high portion of the connecting pipe. In one preferred embodiment of the invention, this pressure-equalizing mechanism comprises a vacuum-breaking vent line with necessary valving extending from the top of the rst stage reactor to a high point in the syphon system, which inl cludes the upwardly extending portion of the drain pipe andthe following downwardly extending portion having its` outlet port substantially lower than the intake port in the bottom of the first stage reactor.

Referring now to the drawings, there is shown in Pig. l one preferred arrangement of elements embodied in the'present invention. In'this Fig. 1, the first stage reactor is indicated at 10 as feeding a number of second stage reactors 12 by means of suitable pipes 14. The rst Istage reactor comprises a reaction chamber 16 containing a charge of molten salt 18 within which there is achieved a partial reduction of titanium tetrachloride to 4 agitated by means of a stirrer 24 carried on a hollow rotating shaft 26 which is driven by a motor 28. This j shaft 26 is preferably provided with means for cooling .byvgas or liquid (not shown) and the stirring provides for a relatively uniform solution of titanium lower chloride in the by-product sodium chloride. The walls of the first stage reactor are preferably chilled so as to maintain a .protective layer of frozen salt thereon (see Fig. 3).

Each of the connecting pipes 14 preferably constitutes a syphon fluid transfer system and includes an upwardly extending portion 30 and a downwardly extending portion 32, the junction of these two portions including a 4lip 33 and a top portion 34 to which a pressure-equalizing line with provisions for opening or closing is connected. The pressure in the pressure-equalizing line is vpreferably controlled by means of a valve 37 which can either connect lthe line to the space above the level of the salt in the first stage reactor, or can connect the pipe 36 to an exhausting device such as a vacuum pump or to i a supply 39 of a pressurized, inert gas such as argon. A

heating coil 38 is provided around drain pipe sections 3 0-32, and a cooling coil 40 is provided about one section of the upwardly extending pipe portion 30.

The second stage reactor 12 preferably comprises a reaction chamber 41 adapted to carry a predetermined charge of molten salt 18 whose titanium chloride conu tent is gradually reduced to titanium crystals by means of sodium added through a pipe 42 and uniformly dis tributed across the surface of the fused salt by means of a spinning disc 44 carried by a rotating shaft 46 of the type more fully described and claimed in the copendng application of Hellier, Serial No. 442,525, led July 12, 1954. Suitable flanges are provided as indicated at 47 for connecting the pipe 14 to the reactor 12. Each second stage reactor 12 is preferably arranged so that the salt charge therefrom can be drained through a passage 48 past a valve 50 into a sump 51.

This valve 50, as shown in greater detail in Fig. 2, preferably includes a cylindrical tube 49 which communicates with the side of the passage 48 and carries a hollow plug 52 which can be moved from a completely retracted position within tube 49 into a position where it nearly completely blocks the passage 43. In Fig. 2, the plug 52 is shown in its passage-blocking position. This hollow plug 52 has a tapered end 54 and preferably includes an internal refrigerant distribution passage 56 through which a refrigerant such as water or the like may be fed to refrigerate the plug and thus freeze the molten salt surrounding the plug in the unblocked portion of the passage 4S. The coolant, which is either a gas or a suitable fluid such as water, Dowtherm or liquid metal, enters the hollow plug through a tube 58 and departs through a tube 60 so that the maximum chilling is achieved adjacent the tapered end 54. A packing 62 is preferably provided near the exterior end of the cylindrical tube 49 so as to prevent leakage of air into the system. A shown, this packing is preferably far removed from the molten salt 18. A positive pressure of an inert gas such as argon is provided by means of an inlet 63 so as to furnish an inert gas bleed inwardly through the packing 62. This prevents travel of the salt 18a up to the packing 62 and prevents damage to the packing by the high temperature of the salt and/or freezing up of the molten salt within the packing. An electric furnace (shown in dotted lines) is preferably provided around the cylindrical tube 49 and the adjacent portion of the tube 48 so as to permit remelting of the frozen salt plug when it is desired to empty the second stage reactor.

That portion of the passage 48 leading from the valve 50 to the sump 51 is so arranged that an effective heat barrier is provided which permits high temperature operation of this portion of the equipment to prevent unwanted freezing of the owing salt while still providing for the use of gasketed connections near these high temperature portions. This heat barrier is formed of a downwardly extending pipe 64 communicating with the passage 48, this pipe 64 being inwardly spaced from the walls of a tube 66 communicating with the top of sump 51. Due to this arrangement, the pipe 64 guides' the hot molten salt in a narrow stream indicated at 18h which is spaced from the tube 66. Accordingly, pipe 64 can be at the temperature of the molten salt (e. g., 850 C.) while the bottom of the tube 66 can be maintained at 100` C. or less, this being particularly true when tube 66 is made of thin-walled stainless steel tubing which has relatively poor heat conductivity.

As mentioned briefly above, the wall of the rst stage reactor is preferably protected from contact with titanium tetrachloride by means of a layer 18e of frozen salt. This layer of frozen salt is preferably maintained in position by means of anchoring studs 70 or other metallic protrusion made of thermally conductive material and attached to the cooled wall in such a manner that an eiicient heat transfer furnishing a low temperature gradient between anchoring means and wall is secured. In one preferred embodiment, as shown more clearly in Fig. 3, these studs 70 can be on the order of 1A: inch to 1 inch in length and are welded to the inner wall 72 of the reactor 10. Because of the intimate heat transfer from the wall to the large surface of the studs 70, the frozen salt layer may bc maintained by forced circulation of a cooling liquid, such as diphenyl or the like, in a suitable cooling channel 74 provided by means of an exterior wall 76. Because the heat conductivity of solidiiied salt is much lower than that of the metal wall and the anchoring studs, the frozen salt layer 18e represents an effective heat barrier which will consume the major part of the temperature drop between the molten salt bath and the cooling medium. At a given release of exothermic heat by the reaction within the molten salt medium, the frozen salt layer 18e will assume a definite thermal equilibrium thickness of frozen salt. lf the released reaction heat and, consequently, the heat ilux is high, the frozen salt heat barrier melts awayuntil suiciently thin to remove substantially all the heat. If the heat ux is low, the frozen salt regenerates its thickness until a new equilibrium is reached. This frozen salt layer constitutes not only an efficient means for reducing the operation temperature of the reactor wall (containing molten salt at a high temperature) to normal operating limits of construction, but it also provides a self- A regenerating, non-contaminating refractory lining for the reactor.

In a preferred embodiment of the invention, when sodium chloride is utilized as the salt 18, an initial layer 18e of sodium chloride, in paste form, may be applied to the studs 70. The paste is then dried to bond the salt to the anchoring studs 70 and to remove any moisture. During operation of the first stage reactor, the exterior of wall 72 is preferably maintained at about 300 F. by the intensive heat exchange with the cooling uid passing through channel 74. Meanwhile, the exothermic reaction taking place within the fused salt 18 will maintain the main body of this salt molten and will provide Ia relatively high ux through the frozen salt layer. This heat ilux can be as high as 40,000 B. t. u. per hour per square foot while still maintaining a layer of frozen salt 18c of about 0.35 inch in thickness.

In the operation of the complete equipment illustrated n Figs. 1, 2 and 3, the apparatus is treated so as to remove all air and water vapor such as yby evacuating and/ or purging by an inert gas such as argon. A charge of molten anhydrous salt sufficient to ll all of the upwardly extending portions 30 of the tube 14 to the level indicated in Fig. 1 is then preferably poured into the reactor. Because the pressure-equalizing lines are open, the level in the reactor 10 and the risers 30 will be identical as in communicating vessels. If this initial level is below the over ow line 33, the riser or risers 30 are lled with stagnant molten salt. If desired, this initial salt charge may be a eutectic salt mixture having a melting point less than that of pure sodium chloride. The stagnant molten salt content in the riser can be used to form the various frozen salt plugs in the upwardly extending portions 38 by operating the cooling coils 40 so that all of the secondary reactors are isolated from the first stage reactor. Sodium and titanium tetrachloride are then fed into the first stage reactor, the titanium tetrachloride being preferably fed below the surface of the salt and the sodium being preferably fed above the surface of the salt. It is also preferred that slightly less than two moles of sodium be fed for each mole of titanium tetrachloride. During this feed, the salt is stirred by means of an agitator 24 so as to provide a uniform solution of titanium lower chloride in the salt. When the reaction has continued for a few hours so as to Iprovide a relatively large mass of titanium lower chloride dissolved in sodium chloride within the molten salt inventory of the reactor 10, the melt level will have risen above syphon overow 33. If one of the salt plugs 18a is then melted out by energizing the heating coil 38 in the upwardly extending pipe 30 and if the pressure-equalizing line 36 is closed, the syphoning effect will empty most of the salt solution from the reactor 10 into the secondary reactor 12, this solution passing through the heated line 14 and being stopped from further travel by means of frozen salt plug 18a in the passage 48 at the bottom of the secondary reactor 12. When a suicienttcharge of titanium lower chloride and sodium chloride has been fed to the secondary reactor 12, the upward ow of salt solution in the -pipe is stopped by breaking the vacuum in the upper section of the syphon venting pipe 36 to the top of the reactor by means of valve 37. If desired, at any time while the salt in pipe 30 is still molten, they syphoning action can be restored by application of suction to the space 34 by means of valve 37 and a vacuum pump (not shown). When the flow of molten salt is discontinued, reactor 10 can be sealed from reactor 12 by forming the frozen salt plug. Cooling uid is then passed through the cooling coil 4i) to freeze the immobilized salt solution in the pipe 30, thereby reestablishing the salt plug 18a. Operation of the first stage reactor is then continued to form another charge of titanium lower chloride dissolved in sodium chloride. When the predetermined charge has thus been formed and the level in the reactor 10 has risen above the overow lip 33, the salt plug is melted and the charge is directed into another secondary reactor 12, as mentioned previously. Meanwhile, slow reduction of the titanium lower chloride contained in one or more of the secondary reactors 12 is being achieved by introducing sodium through the pipe 42 onto the spinning disc 44 so as to provide uniform distribution of the sodium across the surface of the fused salt mass. In a preferred embodiment of the invention, the secondary reduction takes place over a long period of time, on the order of a number of hours, so as to provide for the growth of relatively large crystals of titanium having low surface activity. When reduction has been substantially completed, the valve S0 at the *bottom of the second stage reactor is preferably opened so as to dump the by-product salt into the sump 51. This is preferably achieved by stopping the flow of the cooling medium to the interior of the valve 50 so as to permit the melting of the salt surrounding the hollow plug S2. This melting may be speeded up by intensifying the heating in the furnace. The plug 52 can then be withdrawn so as to permit ow of the molten salt into sump 51 along the line 18b as illustrated in Fig. 2. The secondary reactor, drained of most of its salt, lmay then be removed from the system by breaking the downwardly extending pipe 32 at the ange 47, this tiange being isolated from the hot salt by means of a heat barrier 66a similar to that illustrated in greater detail at 66 in Fig. 2. The contained titanium can be taken out, preferably by first water leaching with an acidied water spray jet. The secondary reactor is then preferably cleaned and a charge of molten salt is then poured into the tube 48 with the plugging means in the position shown in Fig. 2 and while water is circulated within the plug so as to freeze the molten salt running into contact with the plug 52. This reestablishes the frozen salt plug 18a at the bottom of the second stage reactor so that this reactor will be ready for another charge of lower chloride and molten salt.

The apparatus described above is preferably made ofV Inconel or nickel so as to be resistant to the corrosive action of titanium chlorides and sodium chloride or other halides employed. The apparatus is preferably run at atmospheric pressure or with a slight positive pressure of an inert gas such as argon. When the reaction mass comprises sodium chloride, a temperature on the order o-f 800 C. is preferred. A temperature somewhat lower than this Imay be maintained in the rst stage reactor due to the eutectic formed by the titanium lower chlorides and sodium chloride. When halides of alkali metals and alkaline earth metals or mixtures thereof are used, numerous other temperature ranges can be employed. Quite low temperatures may be utilized when eutectic salt mixtures are provided. Numerous reducing agents other than the sodium or sodium-potassium alloy can be employed. For example, magnesium, calcium, lithium and various combinations of these elements may be utilized.

From the standpoint of cheapness, sodium, sodiumpotassium alloy or magnesium are preferred. Other halides of titanium may be utilized, although from the standpoint of cost, ease of handling, etc., the tetrachloride is preferred.

The' present invention can 'be equally employed for the manufacture of other refractory metals by the reduction of suitable compounds carried in a fused salt. It can also be employed in the reduction of alloys, e. g., by the coreduction of several -metallic compounds. alloy of titanium is to be formed, a chloride of a metal such as vanadium, chromium, manganese, iron and the like can be coreduced with the chloride of titanium. The same applies with respect to numerous other metallic elements. In this case, the alloy may be a binary alloy or it may be an alloy containing three, four or more constituents.

The salt mixture, as mentioned previously, can be formed of numerous halides of the alkali metals or alkaline earth metals and the salt can be a. single halide or formed of a number of mixed halides. It can additionally include halides of materials other than the specific reducing agent or agents employed in the reaction. From the standpoint of simplicity of opera-tion and ease of control, it is preferred, however, that the salt be the chloride of the reducing agent or agents employed.

lt should be pointed out, in connection with a consideration yof the various salts which can be employed, that thesesalts should be completely anhydrous and free of any contaminants such as carbon, nitrogen, oxygen or hydrogen, this being particularly true when titanium is to be formed, due to the tremendous reactivity of titanium metal at temperatures lon the 'order of 800 C.900 C. and above.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involve-d, it is intended that all matter contained in the above description, and shown in the accom panying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. Apparatus for producing a refractory metal by the reduction of a compound thereof carried in a molten salt, said apparatus comprising a first stage reactor, a plurality of second stage reactors, a plurality of pipes leading from the first stage reactor, each of said pipes connecting a second stage reactor with the iirst stage reactor, a portion of each of said pipes extending upwardly, means for providing a sufficient gas pressure on the surface of the molten salt in the upwardly extending portion of each pipe to overcome the hydrostatic salt pressure in the reactor to thereby stop the iiow of salt through the pipe, and cooling means associated with each pipe for freezing the stationary salt to create a frozen salt plug in each pipe.

2. Apparatus for producing a refractory metal by the reduction -of a compound thereof carried in a molten salt, said system comprising a lirst chamber, a second chamber, means defining a passage for molten salt connecting said two chambers, means for partially plugging the passage, and means for feeding a refrigerant to the interior of the plugging means.

3. Apparatus for producing a refractory metal by the reduction of a. soluble compound thereof carried in a molten salt, said system comprising a first stage reactor, a plurality of second stage reactors, a plurality of pipes leading from the first stage reactor, each of said pipes connecting a second stage reactor with the first stage reactor, a portion of each said pipe being higher than the bottom of the first stage reactor, means providing sufficient pressure' on the surface of the salt in the high portion of each pipe to overcome salt pressure from the reactor and there by stop flow of salt through the pipe, means associated with each pipe for freezing the thus immobilized salt in each pipe, and means associated with each pipe for melting frozen salt in each pipe.

Thus, if an 4. Apparatus for producing a refractory metal by the reduction of a soluble compound thereof carried in a molten salt, said system comprising a first chamber, a second chamber, means defining a passage for molten salt connecting said two chambers, a hollow plug movable into a position where it at least partially plugs said passage, and means i'or circulating a refrigerant to the interior of said plug for freezing molten salt in the partially plugged passage.

S. Apparatus for producing a refractory metal by 'the reduction of a soluble compound thereof carried in a molten salt, said system comprising a first chamber, a second chamber, means defining a passage for molten salt connecting said two chambers, an elongated hollow plug carried by a side tube communicating with said passage, said plug being mounted for retraction into said side tube to permit free iiow of molten salt through said passage, said plug being movable from its retracted position to a position Where it at least partially plugs said passage, and means for circulating a refrigerant to the interior of said plug for freezing molten salt in the partially plugged passage.

6. Apparatus for producing a refractory metal by the reduction of a compound thereof carried in a molten salt, said system comprising a rst chamber, a second chamber, means defining a passage for molten Isalt connecting said two chambers, means for preventing salt from flowing through the passage, means providing a flanged joint having a gasket, and means for maintaining the gasket at a temperature much below the melting point the molten salt, said last named means comprising a downwardly extending pipe for directing flowing salt in a downwardly extending predetermined path, a second pipe, serving as a heat barrier, surrounding and being spaced from said path,

8 the top of said second pipe being secured to said downwardly extending pipe and the bottom of said second pipe being secured to said ange joint.

7. Apparatus for producing a refractory metal by the reduction of a compound thereof carried in a molten salt, said system comprising a iirst chamber, a second chamber, means defining a passage for molten salt connecting said two chambers, means for preventing salt from owing through the passage, means providing a anged joint having a gasket, and means for maintaining the gasket at a temperature much below the melting point the molten salt, said last named means comprising a downwardly extending pipe for directing owing salt in a free-.owng vertical path, a second pipe, serving as a heat barrier, surrounding and being spaced from said path, the top of said second pipe being secured to said downwardly extending pipe and the bottom of said second pipe terminating in an outwardly extending flange forming a part of said iianged joint.

References Cited in the le of this patent UNITED STATES PATENTS 1,904,664 Neuhauss Apr. 18, 1933 1,935,916 Ragsdale Nov. 21, 1933 2,255,549 Kruh Sept. 9, 1941 2,587,793 Waldron Mar. 4, 1952 2,688,682 Bell Sept. 7, 1954 2,707,313 McShurley et al. May 3, 1955 2,735,668 Gruber et al Feb. 21, 1956 2,756,043 Fleiszar July 24, 1956 FOREIGN PATENTS 243,812 Great Britain Dec. 7, 1925 

2. APPARATUS FOR PRODUCING A REFRACTORY METAL BY THE REDUCTION OF A COMPOUND THEREOF CARRIED IN A MOLTEN SALT, SAID SYSTEM COMPRISING A FIRST CHAMBER, A SECOND CHAMBER, MEANS DEFINING A PASSAGE FOR MOLTEN SALT CONNECTING SAID TWO CHAMBERS, MEANS FOR PARTIALLY PLUGGING THE PASSAGE, AND MEANS FOR FEEDING A REFRIGERANT TO THE INTERIOR OF THE PLUGGING MEANS. 